Evidence for a differential avidity model of T cell selection in the thymus

The specificity of TCR-MHC interaction during positive selection is decided by the recognition of peptides by TCRs. The number of TCRs involved in peptide-MHC complexes is decided by the avidity between the two cell surface components, which in turn decides the fate of thymocytes. Moderate number of TCR leads to positive selection, while a high number results in negative selection.